Most implantable cardiac pacing devices rely on a power source having a limited amount of energy. To conserve energy, and enhance device longevity, such devices often use an energy level that is just sufficient to pace the heart. However, this energy level may vary over time due to a variety of factors. Consequently, various algorithms have been developed to adjust the energy level, periodically or as needed. As described herein, such algorithms are referred to as threshold search algorithms as they typically search for or uncover an energy level that approximate the threshold energy level required to pace the heart.
When an implantable cardiac pacing device delivers energy to the heart and, in response, the heart contracts in a manner akin to a natural contraction, the delivered energy or pacing pulse is said to have captured. Of course, the delivery of energy is typically timed to correspond to a non-refractory period and to avoid inducing arrhythmia. If the heart does not contract, for any of a variety of reasons, then the delivered energy or pacing pulse is said to have not captured. Threshold search algorithms rely on an ability to distinguish capture and non-capture. At a minimum, they must be able to decide whether capture occurred or to decide whether non-capture occurred. Various threshold search algorithms may include features to decide, independently, whether capture or non-capture occurred.
As described herein, various exemplary methods, devices, systems, etc., use morphology to distinguish capture and non-capture. Such exemplary technologies may infer non-capture when capture is not verified (e.g., morphology fails to verify capture) or infer capture when non-capture is not verified (e.g., morphology fails to verify non-capture). Various exemplary technologies optionally include features to verify capture and to verify non-capture.